Field of the Invention
The present invention relates to an anti-vibration apparatus on which an object to be vibration-damped and isolated from vibrations is mounted and, more particularly, to an active anti-vibration apparatus used in precision equipment such as a semiconductor exposure apparatus having a moving mechanism, e.g., an X-Y stage. The present invention also relates to an exposure apparatus having this anti-vibration apparatus and a device manufacturing method using the exposure apparatus. In addition, the present invention relates to anti-vibration method of mounting an object to be vibration-damped and isolated from vibrations.
With improvements in the preciseness of precision equipment such as an electron microscope and a semiconductor exposure apparatus, enhancement of performance of precision anti-vibration apparatuses that mount them has been demanded. In a semiconductor exposure apparatus, in particular, an anti-vibration table from which external vibrations from a pedestal, (apparatus installation pedestal) such as a floor which the apparatus is mounted, are removed as much as possible, is required to realize proper and quick exposure. This is because vibrations that adversely affect exposure must be prevented from being produced in the exposure stage.
In a semiconductor exposure apparatus characterized by intermittent motions, such as step & repeat motions, the repetitive step operation of the X-Y stage induces vibrations of the anti-vibration table. This is because a driving reaction force of the X-Y stage and the load movement of the X-Y stage induce vibrations of the anti-vibration table. The anti-vibration table is, therefore, required to have an anti-vibration function against external vibrations from a pedestal such as a floor on which the apparatus is installed and a vibration control function against vibrations caused by the motions of the equipment mounted on the anti-vibration table.
Some semiconductor exposure apparatuses use the scan exposure scheme instead of the step & repeat scheme. In such an apparatus as well, externally transmitted vibrations such as vibrations from the apparatus installation pedestal must be removed as much as possible, and vibrations of the anti-vibration table which are induced by the scanning operation of the exposure stage must be instantaneously damped. In a scan exposure apparatus, in particular, since exposure is performed while the exposure stage is performing a scanning operation, both the anti-vibration function against external vibrations and the vibration control function against vibrations caused by the motions of the equipment mounted on the anti-vibration table must meet strict requirements. An anti-vibration apparatus with higher performance becomes indispensable.
To meet such requirements, an active anti-vibration apparatus has recently been put into practice, which detects vibrations of an anti-vibration table through a sensor, and compensates for the output signal from the sensor to feed back the resultant signal to an actuator for applying a control force to the anti-vibration table, thereby actively controlling the vibrations of the anti-vibration table. An active anti-vibration apparatus can realize an anti-vibration apparatus having the anti-vibration function and the vibration control function with a good balance, which is difficult for a passive anti-vibration apparatus comprised of springs, dampers, and the like to realize.
As an actuator for applying a control force to an anti-vibration table, a conventional active anti-vibration apparatus generally uses a pneumatic actuator for actively controlling a thrust to be generated by adjusting the internal pressure of a pneumatic spring.
In an anti-vibration apparatus that mounts precision equipment, to maximize the anti-vibration function by minimizing the natural frequency of a vibration system constituted by an anti-vibration table and a support mechanism for damping/supporting the anti-vibration table, it is effective to increase the weight of the anti-vibration table and use pneumatic springs, having a small spring constant, for the support mechanism of the anti-vibration table. In addition, the pneumatic springs can easily generate large thrusts by increasing their pressure-receiving areas, and hence, can be suitably used as a support mechanism for supporting a heavy anti-vibration table. If, therefore, a pneumatic actuator is used as an actuator for applying a control force to an anti-vibration table, an anti-vibration apparatus having a relatively simple structure can be realized because the actuator can also serve as a damper support mechanism for the anti-vibration table.
When, however, a device having a driving means such as an X-Y stage is mounted on an anti-vibration table, as in a semiconductor exposure apparatus, the required vibration suppressing effect cannot always be obtained by an active anti-vibration apparatus using a pneumatic actuator.
In general, an X-Y stage has a mechanism for driving a ball screw by using an electromagnetic motor or a structure of linearly driving the stage by using an electromagnetic linear motor or the like. That is, the X-Y stage is driven by using an electromagnetic actuator exhibiting fast-response characteristics with respect to a driving force command signal. In contrast to this, the response of the pneumatic actuator to a driving force command signal is slower than that of the electromagnetic actuator. In general, the response frequency of the pneumatic actuator is lower than that of the electromagnetic actuator by 100 times or more. For this reason, the active anti-vibration apparatus using the pneumatic actuator cannot generate a control force corresponding to a driving reaction force of the X-Y stage driven by the electromagnetic actuator at a satisfactory response speed, thus failing to obtain a sufficient vibration suppressing effect.
In order to solve such a problem, an electromagnetic actuator may be used as an actuator for applying a control force to an anti-vibration table. For example, as such an apparatus, an anti-vibration apparatus designed to magnetically float the anti-vibration table by using the attraction force of an electromagnet is available. As described above, however, the anti-vibration table that mounts precision equipment is very heavy, and hence, very high energy must be applied to the apparatus to support/drive the anti-vibration table with an electromagnetic force. In the electromagnetic actuator, in particular, heat is generated by coil windings used to generate an electromagnetic force. If, therefore, the actuator is driven by applying high energy, a large quantity of heat is generated. But, precision equipment including a semiconductor exposure apparatus and the like is greatly influenced by changes in temperature; the apparatus performance is seriously affected even by a 1.degree. C. rise in apparatus temperature. Therefore, it is unfavorable if the electromagnetic actuator produces a large amount of heat.
As higher preciseness and throughput are required for semiconductor exposure apparatuses, there are great demands for an active anti-vibration apparatus that can support a heavy anti-vibration table and equipment mounted thereon and generate a control force in quick response to a driving reaction force of a device such as an X-Y stage which is driven on the anti-vibration table at high speed. Such requirements have become stricter in the field of next-generation semiconductor exposure apparatuses and the like, in which it is expected that a driving reaction force of an X-Y stage will increase with an increase in driving speed.
When vibrations produced by such a driving reaction force are to be damped and controlled by using an anti-vibration apparatus, damping and vibration control operation must be performed not only in the vertical direction but also in the horizontal direction. In a semiconductor exposure apparatus or the like, importance is often attached to the integration of an anti-vibration apparatus as a unit. In addition, it is difficult for a conventional anti-vibration apparatus using an air cylinder to perform damping and vibration control in both the vertical and horizontal directions. To realize this, the apparatus inevitably increases in complexity. Demands have, therefore, arisen for an anti-vibration apparatus that is made up of more compact components and appropriately integrated with an exposure apparatus with the components being efficiently arranged.